In the field of the invention, it may be considered that cycle frames can be subdivided into two families, depending on the embodiments concerned.
The first family concerns frames made up by assembling separate elements together, and the second family concerns frames made as single pieces, generally by molding.
The construction of a cycle frame must take into consideration three structural constants that may be considered as unavoidable. They are the length of the rear fork which depends on the radius of the wheel, the angle between the rear fork and a line interconnecting the crank socket and the saddle tube, and the angle of the front fork relative to a horizontal plane.
Although the above three structural characteristics are constant, it will be understood that the height of the frame, i.e. the distance between the crank socket and the top member of the frame, and also the length or projection of the frame, i.e. the distance between the saddle tube and the steering swivel, are values that are essentially variable if the size of the frame is to be adapted as well as possible to the morphological characteristics of the cyclist. Indeed, such adjustment is a prerequisite for cycling to be performed under good conditions and for optimum physical performance to be achieved.
With the first family of frames, satisfying the above structural conditions, both the constant conditions and the variable conditions, is not a real problem. It suffices to have frame elements available that are cut to the desired length in order to be able to assemble a frame that satisfies looked-for characteristics.
On most occasions, such a first family frame makes use of elements that are based on metal tubes or on tubes of so-called synthetic or plastics material such as those made of glass fiber or of carbon fiber.
However, in the second family which corresponds to a frame obtained by molding, satisfying both the constant and the variable structural conditions leads inevitably to a requirement for as many molds as there are to be different frames, if satisfaction is to be given to all requests.
It will readily be understood that it is difficult to make such a requirement compatible with acceptable costs. That is why molded frames are generally made on a one-off basis and are restricted to top level sporting applications.
Such a limit on implementation is not compatible with novel techniques of manufacture that make it possible to implement, by molding, a frame of composite material that is light in weight and particularly strong, being capable of providing performance levels that are much greater than those which can be achieved by the same cyclist using a conventional frame.
Frames made of composite material are essentially based on materials having a wall of draped and polymerized synthetic cloth surrounding a core made of synthetic resin foam, and more particularly a foam that is referred to as "structural" because of its density and of its mechanical characteristics. As an example of a "synthetic resin" mention may be made of polyurethane.